US2661282A

US2661282A - Iron-phosphorus brazing compact

Info

Publication number: US2661282A
Application number: US123998A
Authority: US
Inventors: Bernard A Daley
Original assignee: Servel Inc
Current assignee: Servel Inc
Priority date: 1949-10-28
Filing date: 1949-10-28
Publication date: 1953-12-01
Anticipated expiration: 1970-12-01

Description

Dec. 1, 195s B. A. DALEY 2,661,282

IRON-PHOSPHORUS BRAzING COMPACT Filed oct. 28, 1949 INVENToR. 5MM/ BY Patented Dec. 1, 1953 IRON -IHOSPHORUS BRAZING `GOIVIIEACT 'Bernard A. Daley, Scott Township, Vanderhurgh vrCounty, Ind., Aassig'nor to Servei, Inc., New "York, N. Y., a corporation-of Delaware Application October .28, 1949, Serial Nn. 123,998

`1 Claim. 1

My invention relates to a brazing compound Yand more particularly to the structural formation of a brazing compound for use in production of ammonia refrigerating apparatus as described in United States Patent No. 2,487,001.

A principal problem presented in production of refrigeration apparatus as described in said patent is the physical structure of the brazing or joint sealing composition. In the instance of an iron-phosphorus alloy, it is known to provide the alloy in powdered form mixed with a binder to form a paste for application at a ljoint before brazing. This requires considerable labor v:for application and control. Wire forms, as in copper bracing. are not feasible because of the brittleness of the subject type of alloy. In attempting to solve this problem, I iirst resorted to the knowledge of metallurgy and tried to obtain a shape by compacting the powdered alloy. This was found unsatisfactory because the resulting molded form is too fragile. This could be overcome by sintering, but this is not economically practical because Ythe fragility is such that it is diicult to remove a compact Afrom its mold without breaking, and sintering in a mold results in very short life of the mold. Being confronted with this problem over a long period of time, I iinally conceived of a new method.

I take a 24 per cent phosphorus alloy in powdered form and mix with it powdered iron in the proportion of one gram of powdered alloy to 1.67 grams of iron powder. As a molding lubricant I add about 2 percent stearic acid. This composition is molded under a pressure of about 60,000 lbs. per sq. in. The resulting molded form is readily removed from the mold and handled. The strength of the molded form can be increased by sintering after removal from the mold, although for some sizes and applications this is not necessary.

The previously described molded form contains about 9 per cent phosphorus. To make a 10 per cent phosphorus composition I mix with one gram of the powdered alloy containing 24 per cent phosphorus, 1.4 grams of iron powder.

The inventive concept is my happy thought of intimately mixing the powdered iron alloy with ordinary powdered iron and placing the mixture under pressure, as explained in detail below.

In the accompanying drawings, Figs. l through 4 are detail sectional views of two forms of a pipe joint before end after brazing with a brazing form embodying my invention.

Figs. 1 and 2 show a sleeve joint which in this specic form is sometimes referred to as a bell and spigot joint. The end of the straight piece 0f pipe 4I Tits snugly within an enlarged end portion 45 of the pipe 42. The space between the parts 4l and 45 is greatly enlarged for purposes of description and is indicated by the lreference numeral 4l. Actually there is a push iit between the end of pipe 4| and the enlarged portion 45 of the pipe 42. This clearance and the preferred tolerances is discussed in more detail in said patent.

Referring to Fig. l there is shown a ring 46 which is molded of a composition as previously described. The ring 45 is preferably an ironphosphorus composition of 9 per cent phosphorus, this percentage being obtained by mixing powdered iron-phosphorus alloy of 24 per cent phosphorus with powdered iron in the ratio of l gram powdered alloy to 1.67 grams of pow" dered iron. This powder mixture with about 2 per cent stearic acid as'lubricant is molded vunder VVa pressure oi. approximately 60,000 lbsyper sq. in.

The ring 46 'is slipped over the pipe 4l and located next the end of the joint between this piece of pipe and the enlarged end 45 of the pipe 42. The temperature is raised by a furnace, by induction heating, or by a torch to a temperature between 2050 and 2l00 F. Thereupon kthe ring 45 fuses and nows by capillarity throughout the space 41, forming a solid ring of sealing materiel 48 as illustrated in Fig. 2. The ring 45 is of such a size that it provides just enough material to rlll the joint and form the circular iillets at the ends of the joint as illustrated in Fig. 2. The appearance of the fillets is visual assurance that the joint is completely sealed. Joints made in this fashion withstand internal pressures in excess of 2500 lbs. per sq. in. without leaking. Photomicrographs of a joint like that in Fig. 2 show that the material of the ring 46 penetrates by diiusion into the walls of the joint in addition to forming a sealing film in the joint itself.

In Fig. 3 is shown a modilied form of the previously described joint between the pipes 4I and 42. Being of the same diameter these pipes are butted and a sleeve 49 is tted over the joint, forming the characteristic reinforced joint section and capillary area. The previously described ring 46 of iron-phosphorus composition is located next one end of the sleeve 49. Upon fusion, the ring material distributes itself by capillary action throughout the joint and forms a solid seal 50 as shown disproportionately enlarged in Fig. 4. j

Reverting now to the inventive concept mentioned at the beginning of this specification, an iron-phosphorus alloy of 10.2 per cent phosphorus has a melting point of l922 F. which is satisfactory for bracing of iron at a temperature around 2100 F. The melting point of iron is in the neighborhood of 2700 F. wherefore the brazing temperature must be well below this value to avoid deformation of the iron parts being brazed. Iron-phosphorus alloys of lower and higher phosphorus content have higher melting points than the eutectic alloy of 10.2 per cent4` phosphorus. When I found.4 that. the compacting of the powdered eutectic alloy was "impractical on account of the fragi-lity vofthe compact, it looked like the end of this project. I did con.- sider the inclusion of a binding material in a compact of the powdered alloy, but dislikedthis namely 2050 F. to 2100 F. or thereabouts without ever having to heat the compact above about 2100 F. I tried it and it worked. This was a valuable discovery because I now had a compact that was strong enough to be handled, a

' compact that was all brazing material, and a on account of the volume of binding material that would ce required compared to the "amount, of actual brazing alloy in each compact.

I knew thaty I could bind the eutectichferrophosphorus powder togetherinto. a compact by introducing sufiicient iron .powder to form a binding matrix, however, the quantity of iron .powder necessary to afford sufficient practical strength would be sufficiently great to dilute Athe eutectic ferro-phosphorus (10.2% phosphorus), when it melted, to the extent that no flow would be obtained.

It seemed hopeless to use a higher phosphorus ferro-phosphorus alloy powder to gain a mixture or" approximately eutectic proportions because with each added increment of phosphorus above the eutectic composition the melting point of the alloy would go up and the temperature F.A which would be muchtoo high for practical use.

Then there ashed .across my mind the possibility that such a compact made up of an intimate mixture of iron powder and high phos- 1" phorus ferro-phosphorus powder in theproper proportions to elect amixture of approximately eutectic composition might work for I visualized that as the temperature of such a compact was increased there might be a diffusion of phoscompact that would melt and flow at the proper temperature. I have found the proportions of powdered alloy and powdered iron may be varied somewhat and yet produce satisfactory results. The reason may be that during the alloying action within the compact during increase in temperature, there occurs locally enough alloy of eutectic proportions to melt and carry with it other metal of the compact by capillarity into the joint being brazed. Y

Various change may be made within the scope of the invention as set forth in the following claim.

I claim:

Powdered alloy of iron and phosphorus having a relative phosphorus content greater than that in a eutectic proportion, and powdered iron mixed with the powdered alloy in such quantities that the relation of iron and phosphous in the whole mixture is substantially a eutectic proportion, the mixture being compacted to a form adapted for application as brazing material to a joint betweeniron parts.

g `BERNARD A. DALEY.

References cited. in the .fue of this patent UNITED sTATEs PATENTS